Method and apparatus for steering and stabilizing radio frequency beams utilizing photonic crystal structures

ABSTRACT

An RF beam steering device employs a prism assembly to steer an RF beam and a compensation device to address undesirable movement of the beam steering device. The prism assembly includes a plurality of dielectric prisms each with an associated impedance matching layer. The dielectric prisms are rotated relative to each other to steer the RF beam in a desired direction and further to compensate for movement of the beam steering device itself. The prisms include a plurality of individual panels with drilled or slotted openings that are arranged to create a periodic photonic crystal structure within a defined region. This configuration effectively alters the dielectric constant over any one particular region of a panel, thereby altering the level of diffraction possible for a specified panel thickness. The openings within each stacked panel are overlapped to produce the required level of diffraction and refractive index gradient. Motors rotate the prisms relative to each other to the correct orientation for steering the RF beam in a desired manner.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 11/734,026, entitled “Method and Apparatus for Steering RadioFrequency Beams Utilizing Photonic Crystal Structures” and filed Apr.11, 2007, which is a Continuation-In-Part of U.S. patent applicationSer. No. 11/693,817, entitled “Radio Frequency Lens and Method ofSuppressing Side-Lobes” and filed Mar. 30, 2007, the disclosures ofwhich are incorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention pertains to steering radio frequency (RF) beams.In particular, the present invention pertains to a device utilizingphotonic crystal structures (e.g., prisms, etc.) to steer or direct RFbeam transmissions.

2. Discussion of Related Art

Radio frequency (RF) transmission systems generally employ dish or otherantennas that reflect RF signals to transmit an outgoing collimatedbeam. The beam may be steered via several conventional techniques. Forexample, motorized gimbal assemblies may be employed that use two motorsand associated feedback circuitry to physically move the antenna (bothin azimuth and elevation) to steer a radio frequency (RF) beam. However,gimbal-steered assemblies are typically heavy and bulky, and requiresubstantial amounts of power to turn the antenna and maintain alignmentof the radio beam. In many cases, the weight of the gimbal-steeredassembly and antenna exceed the load rating of the platform. Further,the closed-loop feedback system used to stabilize a combined antenna andgimbal-steered assembly is complex and requires customization for eachinstallation. In addition, gimbal-steered systems require extremely highlevels of mechanical stability for applications involving narrow radiobeam widths (e.g., millimeter wave radio systems).

Phased-array steering systems may also be employed to steer an RF beam.Generally, theses types of systems employ numerous transmit/receivemodules that each provide a portion of the resultant RF beam. The beamportions are combined and collectively produce the resultant RF beamtransmitted or steered in the desired direction. However, these types ofsystems require a large number of electronic subsystems (e.g., one foreach radiating element or transmit/receive module) to electronicallysteer the beam. Phased-array beam steering systems further broaden theRF beam when moved off of boresight and increase side-lobe levels.Side-lobes are the portion of an RF beam that are a by-product of beampropagation from the aperture of the antenna. Typically, suppression ofthe side-lobe energy is critical for reducing the probability that thetransmitted beam is detected (e.g., an RF beam is less likely to bedetected, jammed or eavesdropped in response to suppression of theside-lobe energy).

In addition, dielectric wedges may be used to steer radio waves throughprismatic diffraction principles. The wedges are preferably constructedfrom homogeneous structures. However, these types of homogenousstructures require that the wedges be machined from blocks of suitablematerials. Typically, this involves the machining of rectangular blocksto form wedges of a specified angle, thereby inherently wasting thematerial.

SUMMARY OF THE INVENTION

According to present invention embodiments, an RF beam steering deviceemploys a prism assembly to steer an RF beam. The prism assemblyincludes a plurality of dielectric prisms each with an associatedimpedance matching layer to deflect the RF beam over a controlled range.The dielectric prisms are rotated relative to each other to steer the RFbeam. The prisms include a plurality of individual panels with drilledor slotted openings that are arranged to produce a photonic crystalstructure optimized for a specific radio frequency. The openings arearranged in each panel to effectively create a periodic photonic crystalstructure within a defined region. This configuration effectively altersthe dielectric constant over any one particular region of a panel,thereby altering the level of diffraction possible for a specified panelthickness. The openings within each stacked panel are overlapped toproduce the required level of diffraction and refractive index gradient.Motors rotate the prisms relative to each other to the correctorientation for steering the RF beam in a desired manner.

The RF beam steering device provides several advantages. In particular,the device utilizes an advanced steering technique. Rather thanphysically moving an entire antenna in both azimuth and elevation toachieve motion compensation, the device simply manipulates the RF beam.The beam movement is accomplished by rotation of two or more dielectricprisms. This simplifies the platform dynamics of the combinedantenna/prism steering assembly. For example, the device may employsmaller, lightweight and lower power motors and a simplified open-loopcontrol system to achieve the same or comparable level of performance ofRF beam steering as the gimbal-steered systems. Further, diffraction ina dielectric media may be realized by varying the index of refractionacross the surface of a flat structure. This allows the prisms to befabricated using conventional circuit board laminate materials modifiedby panel drilling and slotting procedures. The diffraction angle may bevaried by controlling the number and thickness of stacked laminatepanels, the number and spacing of drilled or slotted openings in apanel, and the dielectric constant of the laminate. The hole and slotpatterns control the performance of the prism photonic crystalstructure. In addition, the inherent lightweight nature of the prismdielectric material (and holes defined therein) enables creation of anRF prism that is lighter than a corresponding solid counterpart.

Embodiments of the present invention may also provide a compensationmechanism to account for sway or instability with regard to a platformto which the prisms are mounted. The compensation mechanism may includeaccelerometers to detect roll, pitch or yaw. Multi- or single-axisaccelerometers may be employed. Tilt sensors may also be employed.Alternatively, a mechanical system, including, for example, weightedpendulums may be coupled to the prisms and move in a direction oppositeto the movement of the platform thereby self-correcting the position ofthe prisms.

The above and still further features and advantages of the presentinvention will become apparent upon consideration of the followingdetailed description of specific embodiments thereof, particularly whentaken in conjunction with the accompanying drawings wherein likereference numerals in the various figures are utilized to designate likecomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of the beam steering deviceaccording to a present invention embodiment.

FIG. 2 is a diagrammatic illustration of an exemplary prism of the beamsteering device of FIG. 1 according to an embodiment of the presentinvention.

FIG. 3 is a diagrammatic illustration of an exemplary photonic crystalstructure of the type employed by the prism of FIG. 2 according to anembodiment of the present invention.

FIG. 4A is a perspective view in partial section of an exemplary wedgeprism.

FIG. 4B is a diagrammatic illustration of a beam being steered by theexemplary wedge prism of FIG. 4A.

FIG. 5 is a view in elevation and section of the exemplary wedge prismillustrated in an inverted position with respect to FIG. 4A.

FIG. 6 are views in partial section of the exemplary wedge prism of FIG.4A illustrating a varying wedge angle.

FIG. 7 is a block diagram of an exemplary circuit for stabilizing prismsin accordance with an embodiment of the present invention.

FIG. 8 is a schematic diagram of an exemplary mechanical stabilizationmechanism in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention embodiments pertain to a radio frequency (RF) beamsteering device that includes a plurality of prisms each with a photoniccrystal structure. The prisms are rotated relative to each other tosteer an RF beam in a desired manner as illustrated in FIG. 1.Specifically, beam steering device 50 includes a plurality of prisms 20,21, a plurality of rotating assemblies 23, a plurality of motors 30 anda controller 40. Each prism 20, 21 is fabricated using dielectricmaterials (e.g., RF laminate, etc.) suitable for use in radio frequencyapplications. The prisms are preferably configured to enable thedielectric materials to produce electromagnetic fields that deflect thebeam a desired amount in a particular axis of motion as described below.Each prism includes a prism layer to refract the beam and one or moreimpedance matching layers to enhance radio wave propagation byminimizing reflections. Arrays of hole or slot patterns are definedwithin the dielectric materials of the prism and impedance matchinglayers to create photonic crystal structures that vary the index ofrefraction (e.g., proportional to the dielectric constant of thematerial) over the surface of the prism as described below. The prismlayers are bonded together into a single structure, where successivelayers of dielectric materials, each with a specific dielectricconstant, may be stacked with the appropriate quantity of adhesivelayers (e.g., pre-reg sheets, etc.) to increase the diffraction angle ofthe prism. The impedance matching layers transform the free-space planewave impedance to match the impedance of the higher dielectric constantmaterial. By way of example only, the beam steering device is describedwith respect to two sequential (e.g., first and second) prisms 20, 21.However, the beam steering device may include two or more prisms toperform beam steering with the desired deflection angle.

Prisms 20, 21 are each mounted on a corresponding rotating assembly 23.The rotating assemblies may be implemented by any conventional or otherassemblies, and typically include a rotating mechanism (e.g., rotatingring, platform or other suitable structure) to secure and rotate aprism. The rotating assemblies are each manipulated by a correspondingmotor 30 to rotate the prisms relative to each other to produce thedesired deflection angle for the beam. The motors may be implemented byany conventional or other motors or actuators to rotate the prisms. Byway of example, the beam steering device includes two rotatingassemblies disposed in a manner to position prisms 20, 21 coincidenteach other. This enables an RF beam to sequentially traverse the prismsfor desired steering as described below.

Motors 30 are controlled by controller 40 to rotate the prisms in acertain manner relative to each other to achieve a desired beamsteering. The controller may be implemented by any conventional or othercontroller or processor (e.g., microprocessor, controller, controlcircuitry, logic, etc.), and is basically utilized within a feedbackloop to control prism rotation. For example, the mounting assembliesand/or motors may include one type of sensors 29 to measure andcoordinate prism rotation (other types of sensors are described laterherein). The sensors may be implemented by any conventional or othersensors (e.g., encoders, potentiometers, etc.) to measure the prismrotation and/or other system conditions. These measurements are providedto the controller to enable control of prism rotation and steering ofthe beam.

Basically, an RF beam 7 is provided to beam steering device 50 from asource, such as an antenna 5 transmitting the RF beam. The RF beamtraverses first prism 20 and is refracted by the electromagnetic fieldproduced from the photonic crystal structures of the prism. Therefracted RF beam subsequently traverses second prism 21 and is againrefracted by the electromagnetic field produced from the prism photoniccrystal structures. The orientation of prisms 20, 21 relative to eachother enables the prisms to collectively produce a resulting RF beam 27refracted or steered in the desired direction. Controller 40 controlsmotors 30 to rotate the prisms in a manner to achieve the desiredsteering effect based on the analysis described below (e.g., Equations1-11 to achieve the desired steering angle, θ_(S) or φ). The controllermay manipulate both prisms simultaneously to achieve the desiredorientation, or one prism may be stationary while the other prism ismanipulated.

An exemplary prism structure according to an embodiment of the presentinvention is illustrated in FIG. 2. Specifically, each prism 20, 21includes a prism portion or layer 10 and a plurality of impedancematching layers 22. First prism 20 may further include an absorbing orapodizing layer or mask 24 to reduce side-lobes. These layers eachpreferably include a photonic crystal structure (e.g., dielectric orabsorbing materials with a series of holes defined therein) as describedbelow. Prism layer 10 is disposed between and attached to impedancematching layers 22 via pre-preg sheets 33 (e.g., glue or other adhesivesheets) and/or other suitable adhesives. An RF beam enters prisms 20, 21and traverses an initial impedance matching layer 22 and prism layer 10,and exits through the remaining impedance matching layer as a steeredbeam. Apodizing mask 24 may be attached to first prism 20, via pre-regsheet 33, to a surface of an impedance matching layer 22 that faces asignal source (e.g., antenna 5 as viewed in FIG. 1). In this case, theRF beam enters first prism 20 and traverses apodizing mask 24, aninitial impedance matching layer 22 and prism layer 10, and exitsthrough the remaining impedance matching layer as a steered beam.However, the layers of prisms 20, 21 may be of any quantity and may bearranged in any suitable fashion. Further, additional dielectric and/orabsorbing materials and/or pre-reg sheets may be used to adjust theoverall thickness of one or more prism layers.

Prism layer 10 includes a photonic crystal structure. An exemplaryphotonic crystal structure for prism layer 10 is illustrated in FIG. 3.Initially, photonic crystal structures utilize various materials, wherethe characteristic dimensions of, and spacing between, the materials aretypically on the order of, or less than, the wavelength of a signal (orphoton) of interest (e.g., for which the material is designed). Thematerials typically include varying dielectric constants. Photoniccrystal structures may be engineered to include size, weight and shapecharacteristics that are desirable for certain applications.Specifically, prism layer 10 is formed by defining a series of holes 14within a parent material 12, preferably by drilling techniques. However,the holes may alternatively be defined within the parent material viaany conventional techniques or machines (e.g., computer-aidedfabrication, two-dimensional machines, water jet cutting, laser cutting,etc.). In this case, the two materials that construct the photoniccrystal structure include air (or possibly vacuum for spaceapplications) and parent material 12. The parent material is preferablyan RF laminate and includes a high dielectric constant (∈_(r); e.g., inthe range of 10-12). The parent material may alternatively includeplastics (e.g., a high density polyethylene, etc.), glass or othermaterials with a low loss tangent at the frequency range of interest anda suitable dielectric constant. The hole arrangement may be adjusted toalter the behavior of the prism layer as described below.

Parent material 12 may be of any suitable shape or size. By way ofexample only, parent material 12 is substantially cylindrical in theform of a disk with substantially planar front and rear surfaces. Theholes are generally defined through the parent material in the directionof (or substantially parallel to) the propagation path of the beam(e.g., along a propagation axis, or from the prism front surface throughthe prism thickness toward the prism rear surface). Holes 14 withinparent material 12 include dimensions less than that of the wavelengthof the signal or beam of interest, while the spacing between these holesare similarly on the order of or less than the interested signalwavelength. For example, a hole dimension and spacing each less than onecentimeter may be employed for an RF beam with a frequency of 30gigahertz (GHz). A greater efficiency of the prism may be achieved byreducing the dimensions and spacing of the holes relative to thewavelength of the signal of interest as described below.

As a photon approaches material 12, an electromagnetic field proximatethe material essentially experiences an averaging effect from thevarying dielectric constants of the two materials (e.g., material 12 andair) and the resulting dielectric effects from those materials areproportional to the average of the volumetric capacities of thematerials within the prism layer. In other words, the resultingdielectric effects are comparable to those of a dielectric with aconstant derived from a weighted average of the material constants,where the material constants are weighted based on the percentage of thecorresponding material volumetric capacity relative to the volume of thestructure. For example, a structure including 60% by volume of amaterial with a dielectric constant of 11.0 and 40% by volume of amaterial with a dielectric constant 6.0 provides properties of adielectric with a constant of 9.0 (e.g.,(60%×11.0)+(40%×6.0)=6.6+2.4=9.0).

Since an optical prism may include portions of greater refractivematerial, the photonic crystal structure for prism layer 10 may beconstructed to similarly include (or emulate) this property. By way ofexample only, holes 14 may be defined within a portion of the prismlayer to be spaced significantly closer together than holes definedwithin other prism layer portions, where the dielectric constant of theprism layer, ∈_(r), increases from the portion with closely spaced holesto the portion with further spaced holes (e.g., as viewed in FIG. 3).Since the index of refraction of the prism layer is proportional to thedielectric constant, the index of refraction similarly follows thistrend. The spacing of holes 14 and their corresponding diameters may beadjusted as a function of the structure diameter to create a prismeffect from the entire structure. Thus, the electromagnetic fieldsproduced by the photonic crystal structure essentially emulate theeffects of an optical prism and enable the entire RF beam to be steeredor refracted. Since the photonic crystal structure is generally planaror flat, the photonic crystal structure is simple to manufacture and maybe realized through the use of computer-aided fabrication techniques asdescribed above.

The manner in which holes 14 are defined in prism layer 10 is based onthe desired steering or refraction of the RF beam. An exemplary opticalwedge prism 25 that steers or refracts a beam is illustrated in FIGS.4A-4B and 5-6. Initially, prism 25 is substantially circular andincludes a generally triangular (or wedge shaped) transversecross-section (FIG. 4A) providing a wedge angle (e.g., varying prismthicknesses along a vertical optical axis 80, where the wedge angle isdefined by the wedge or prism narrow portion) for purposes of describingthe steering effect. The various prism thicknesses enable the wedgeangle to vary at successive angular prism locations relative to theprism optical axis (e.g., the wedge angle varies at prism rotations of0°, 10°, 20°, 30° and 45° relative to the optical axis as viewed in FIG.6). A cross-section of prism 25 includes a base and a truncated vertexdisposed opposite the base (FIG. 5) with exterior prism faces orientedat the wedge angle and not perpendicular to an axis of rotation 60 ofthe prism (e.g., the axis about which the prism is rotated, typicallythe axis extending through the centerpoints of the prism faces).

Specifically, a beam 7 is directed to traverse prism 25. The propagationof the beam exiting the prism may be determined from Snell's Law asfollows.

n₁ sin θ₁=n₂ sin θ₂  (Equation 1)

where n₁ is the index of refraction of the first material traversed bythe beam, n₂ is the index of refraction of the second material traversedby the beam, θ₁ is the angle of the beam entering into the secondmaterial, and θ₂ is the angle of the refracted beam within thatmaterial. The steering angles of interest for beam 7 directed towardprism 25 are determined relative to rotation axis 60 (e.g., an axisperpendicular to and extending through the centerpoints of the prismfront and rear faces) and in accordance with Snell's Law. Thus, each ofthe equations based on Snell's Law (e.g., as viewed in FIG. 4B) has theequation angles adjusted by the wedge angle (e.g., β as viewed in FIG.4B) to attain the beam steering value relative to the rotation axis asdescribed below.

Beam 7 enters prism 25 at an angle, θ_(1A), that is within a planecontaining optical axis 80 for the prism (e.g., the vertical line oraxis through the center of the prism point from the thinnest part to thethickest part) and rotation axis 60. This angle is the angle of the beam23 entry, α, relative to rotation axis 60 and adjusted by the wedgeangle, β (e.g., θ_(1A)=α−β). The beam is refracted at an angle, θ_(2A),relative to surface normal 70 of the prism front surface and determinedbased on Snell's Law as follows.

$\begin{matrix}{\theta_{2A} = \left( {\sin^{- 1}\left( {\frac{n_{air}}{n_{M}}\; \sin \; \left( \theta_{1A} \right)} \right)} \right)} & \left( {{Equation}\mspace{20mu} 2} \right)\end{matrix}$

where n_(air) is the index of refraction of air, n_(M) is the index ofrefraction of the prism material and θ_(1A) is the angle of beam entry.

The beam traverses the prism and is directed toward the prism rearsurface at an angle, θ_(1B), relative to surface normal 70 of that rearsurface. This angle is the angle of refraction by the prism frontsurface, θ_(2A), combined with wedge angles, β, from the front and rearprism surfaces and may be expressed as follows.

θ_(1B)=θ_(2A)+2β  (Equation 3)

The beam traverses the prism rear surface and is refracted at an angle,θ_(2B), relative to surface normal 70 of the prism rear surface anddetermined based on Snell's Law as follows.

$\begin{matrix}{\theta_{2B} = \left( {\sin^{- 1}\left( {\frac{n_{M}}{n_{air}}\; \sin \; \left( \theta_{1B} \right)} \right)} \right)} & \left( {{Equation}\mspace{20mu} 4} \right)\end{matrix}$

where n_(M) is the index of refraction of the prism material, n_(air) isthe index of refraction of air, and θ_(1B) is the angle of beam entry.The angle of refraction, θ_(R), relative to rotation axis 60 is simplythe refracted angle relative to surface normal 70 of the prism rearsurface, θ_(2B), less the wedge angle, β, of the prism rear surface(e.g., as viewed in FIG. 4B) and may be expressed as follows.

$\begin{matrix}\begin{matrix}{\theta_{R} = {\theta_{2B} - \beta}} \\{= {{\sin^{- 1}\left( {\frac{n_{M}}{n_{air}}{\sin \left( {{\sin^{- 1}\left( {\frac{n_{air}}{n_{M}}{\sin \left( {\alpha - \beta} \right)}} \right)} + {2\beta}} \right)}} \right)} - \beta}}\end{matrix} & \left( {{Equation}\mspace{20mu} 5} \right)\end{matrix}$

Additional terms are needed in order to extend the formula to a secondsequential prism. In particular, Snell's law is applied to theadditional prism via a projection technique that decomposes RF beam 7refracted by the first prism into X and Y components with respect to anoptical axis of the second prism. The X component of the RF beam isderived from the RF beam exiting the first prism. This beam componentexits the first prism at a given angle, ρ, which may be determined bysetting angle α to zero in Equation 5 as follows.

$\begin{matrix}{\rho = {{\sin^{- 1}\left( {\frac{n_{M}}{n_{air}}{\sin \left( {{\sin^{- 1}\left( {\frac{n_{air}}{n_{M}}{\sin \left( {- \beta} \right)}} \right)} + {2\beta}} \right)}} \right)} - \beta}} & \left( {{Equation}\mspace{20mu} 6} \right)\end{matrix}$

where n_(M) is the index of refraction of the prism material, n_(air) isthe index of refraction of air, and β is the wedge angle.

The optical axis of the second prism may be angularly offset from theoptical axis of the first prism. In this case, the RF beam from thefirst prism needs to be decomposed into the X and Y components. The Xcomponent of the angle of incidence of the RF beam on the second prismcreates an effect on the wedge angle. Basically, the angle of incidencemakes the wedge angle of the second prism appear larger (FIG. 6),thereby causing greater steering effects on the RF beam in the secondprism.

In order to account for the angle of incidence of the RF beam into thesecond prism, and the effective increase in the wedge angle, a new wedgeangle, β_(γ), is derived from the expansion of the wedge angle along theX-axis of the angle of incidence and may be expressed as follows.

$\begin{matrix}{\beta_{\gamma} = {\tan^{- 1}\left( \frac{\tan \; \beta}{\cos \left( {\rho \; \sin \; (\gamma)} \right)} \right)}} & \left( {{Equation}\mspace{20mu} 7} \right)\end{matrix}$

where β is the wedge angle, ρ is the X component of the RF beam exitingthe first prism and γ is the angular offset between the optical axes ofthe first and second prisms. The new effective wedge angle increases theamount the prism steers the beam.

The Y component of the resulting RF beam (e.g., along the Y-axis or axisparallel to the optical axis of the second prism) steered by the secondprism may be determined from Snell's Law and expressed as follows.

$\begin{matrix}{\theta_{y} = {{\sin^{- 1}\left( {\frac{n_{M}}{n_{air}}{\sin \begin{pmatrix}{{\sin^{- 1}\left( {\frac{n_{air}}{n_{M}}{\sin \begin{pmatrix}{{\rho \; \cos \; (\gamma)} -} \\{2\beta_{\gamma}}\end{pmatrix}}} \right)} +} \\{2\beta_{\gamma}}\end{pmatrix}}} \right)} - \beta_{\gamma}}} & \left( {{Equation}\mspace{20mu} 8} \right)\end{matrix}$

where n_(M) is the index of refraction of the material of the prism,n_(air) is the index of refraction of air, β_(γ) is the newly derivedwedge angle, ρ is the X component of the RF beam exiting the first prismand γ is the angular offset between the optical axes of the first andsecond prisms.

Since the X component of the RF beam along the X-axis (e.g., thetransverse axis perpendicular to the optical axis of the second prism)effectively does not see the wedge (e.g., analogous to a sliceperpendicular to the vertical optical axis which provides the samethickness or wedge angle), the X component of the resulting angle forthe steered RF beam is basically unaltered. Thus, the resulting Xcomponent of the steering angle, θ_(X), is produced by the first prismand may be expressed as follows.

θ_(x)=ρ sin(γ)  (Equation 9)

where ρ is the angle of the X component of the RF beam exiting the firstprism and γ is the angular offset between the optical axes of the firstand second prisms.

The magnitude of the resulting steering angle, θ_(S), is given by theroot sum square (RSS) of θ_(X) and θ_(Y) and may be expressed asfollows.

θ_(S)=√{square root over (θ_(x) ²+θ_(y) ²)}  (Equation 10)

Generally, an arbitrary alignment between the optical axis of the secondprism and the field of regard (FoR) is employed in an implementation.The above formulas may be further extended by applying one morecoordinate transformations (e.g., a rotation about the Z-axis or axisparallel with the axis of rotation), where the most general form forsteering the RF beam is obtained and any point within the entire FoR maybe achieved. This may be expressed within polar coordinates in fieldspace as follows.

$\begin{matrix}{\varphi = {{\tan^{- 1}\left( \frac{\theta_{y}}{\theta_{x}} \right)} + \varphi_{0}}} & \left( {{Equation}\mspace{20mu} 11} \right)\end{matrix}$

where φ represents the rotational component of the steering, φ₀represents the rotation between the optical axis of the second prism andthe Field of Regard coordinate system, θ_(X) represents the X componentof the steering angle for the RF beam and θ_(Y) represents the Ycomponent of the steering angle for the RF beam.

Referring to FIG. 5, exemplary optical wedge prism 25 (e.g., invertedwith respect to FIGS. 4A and 6) is symmetric about a plane perpendicularto prism rotation axis 60. Prism 25 typically includes a nominalthickness, t_(m), at the portion proximate the truncated vertex. Theprism includes an index of refraction, n₁, while the surrounding media(e.g., air) includes an index of refraction, n₀, typically approximatedto 1.00. An average index of refraction for prism 25 may be determinedfor a prism portion or line (e.g., along the dashed-dotted line asviewed in FIG. 5) as a function of the distance, y, of that line fromthe base edge of prism 25 as follows (e.g., a weighted average of indexof refraction values for line segments along the line based on linesegment length).

$\begin{matrix}{{\overset{\_}{n}(y)} = \frac{{2{n_{1}\left( {D - y} \right)}\tan \; \beta} + {2n_{0}y\; \tan \; \beta}}{2D\; \tan \; \beta}} & \left( {{Equation}\mspace{20mu} 12} \right)\end{matrix}$

where n₁ is the index of refraction of prism 25, n₀ is the index ofrefraction of air, D is the diameter or longitudinal dimension of prism25, y is the distance from the prism edge and β is the wedge angle ofprism 25. The nominal thickness, t_(m), of prism 25 does not contributeto the average index of refraction since the prism index of refractionremains relatively constant in the areas encompassed by the nominalthickness (e.g., between the vertical dotted lines as viewed in FIG. 5).

The linear change in the average index of refraction of prism 25 as afunction of the distance, y, determines the steering angle of prism 25as follows.

$\begin{matrix}{\frac{\overset{\_}{n}}{y} = {\frac{{2n_{0}\tan \; \beta} - {2n_{1}D\; \tan \; \beta}}{2D\; \tan \; \beta} = {\left( \frac{n_{0} - {n_{1}D}}{D} \right)\tan \; \beta}}} & \left( {{Equation}\mspace{20mu} 13} \right)\end{matrix}$

where n₁ is the index of refraction of prism 25, n₀ is the index ofrefraction of air, D is the diameter or longitudinal dimension of prism25 and β is the wedge angle of prism 25. Therefore, a photonic crystalprism with a constant average index of refraction variation, dn/dy,provides the same beam steering characteristics as wedge prism 25 with awedge angle, β, expressed as follows.

$\begin{matrix}{\beta = {\arctan \left( {\frac{\overset{\_}{n}}{y} \cdot \frac{D}{n_{0} - {n_{1}D}}} \right)}} & \left( {{Equation}\mspace{20mu} 14} \right)\end{matrix}$

where n₁ is the index of refraction of prism 25, n₀ is the index ofrefraction of air and D is the diameter or longitudinal dimension ofprism 25.

In order to create a photonic crystal prism that emulates the physicalproperties of prism 25, a series of holes are arranged within a parentmaterial in substantially the same manner described above to create thedesired average index of refraction profile described above. However,the index of refraction for a photonic crystal prism is equivalent tothe square-root of the prism dielectric constant (e.g., for materialsthat exhibit low loss tangents which are preferred for prism steering ofRF beams). In the case of materials including significant absorption orscatter, the index of refraction is a complex value with real andimaginary components. The imaginary component provides a measure ofloss. Since the magnitude of the imaginary component (or loss) detractsfrom the real component (or dielectric constant), the dielectricconstant differs from the above relationship in response to significantlosses. The effective index of refraction along a portion or line of thephotonic crystal prism is obtained by taking the average volumetricindex of refraction along that line (e.g., a weighted average of theindex of refraction (or dielectric constants of the materials and holes)along the line based on volume in a manner similar to that describedabove). The steering angle, θ_(S) or φ, of the resulting photoniccrystal prism may be determined based on Snell's Law by utilizing theeffective index of refraction of the photonic crystal prism as thematerial index of refraction, n_(M), within the analysis describedabove. The volumetric average determination should consider the regionsabove and below the line (e.g., analogous to distance value, y,described above). The physical shape of the holes may vary depending onthe manufacturing process. One exemplary manufacturing process includesdrilling holes in the prism materials.

The orientation of the holes defined in the photonic crystal prism maybe normal to the front and back prism faces (e.g., in a direction of therotation axis). The dimensions of the holes are sufficiently small toenable the electromagnetic fields of photons (e.g., manipulated by thephotonic crystal structure) to be influenced by the average index ofrefraction over the prism volume interacting with or manipulating thephotons. Generally, the diameter of the holes does not exceed (e.g.,less than or equal to) one-quarter of the wavelength of the beam ofinterest, while the spacing between the holes does not exceed (e.g.,less than or equal to) the wavelength of that beam.

Accordingly, an interaction volume for the photonic crystal prismincludes one square wave (e.g., an area defined by the square of thebeam wavelength) as viewed normal to the propagation axis. Since changesin the photonic crystal structure may create an impedance mismatch alongthe propagation axis, the interaction length or thickness of thephotonic crystal prism includes a short dimension. Generally, thisdimension of the photonic crystal prism along the propagation axis(e.g., or thickness) should not exceed 1/16 of the beam wavelength inorder to avoid impacting the propagation excessively (e.g., by producingback reflections or etalon resonances). Thus, drilling holes through thethickness of the material is beneficial since this technique ensuresminimal change to the index of refraction along the propagation axis.

By way of example, a spacing of holes within the parent material thatprovides a minimum average index of refraction (e.g., defined by thelargest hole diameter allowed and determined by the wavelength ofoperation as described above) includes the holes spaced apart from eachother in a hexagonal arrangement of equatorial triangles (e.g., eachhole at a corresponding vertex of a triangle) with a minimum wallthickness between holes to provide adequate mechanical strength. This isa spacing of holes that coincides with the thinnest part of aconventional prism (e.g., y=D in Equation 12).

Conversely, a spacing of holes within the parent material that mayprovide the greatest average index of refraction is a photonic crystalprism without the presence of holes. However, the need for a smoothlychanging average index of refraction and efficient control of thedirection of the beam energy may put limitations on this configuration.If the photonic crystal prism is configured to include holes of the samesize (e.g., as may be economically feasible due to manufacturinglimitations on machines, such as automated drilling centers), themaximum average index of refraction would be obtained with a minimum ofone hole per interaction volume. This region of the photonic crystalprism corresponds to the thickest part of prism 25 (e.g., y=0 inEquation 12).

The desired prism characteristics (or steering angles, θ_(R) and θ_(S),for the first and second prisms) may be selected, where the prism wedgeangles, β, providing these characteristics may be determined from theabove equations (e.g., Equations 1-11). Once the wedge angle isdetermined, the photonic crystal prisms may be configured with a seriesof holes in accordance with the index of refraction profiles (e.g.,determined from the change and average index of refraction values fromEquations 13-14) providing the desired characteristics of prisms withthose wedge angles. The wedge angle, β, for first and second prisms 20,21 may be the same or different angle depending upon the characteristicsdesired.

Thus, based on a desired steering angle, θ_(S) or φ, for the beam,controller 40 (FIG. 1) may utilize the above equations (e.g., Equations6-11 with the known properties of the prisms (e.g., index of refractionsof the material and air, wedge angle, etc.)) to determine the angularoffset, γ, needed between the first and second photonic crystal prisms,and subsequently control motors 30 to position the prisms in anappropriate fashion to steer the beam in a desired manner.

The photonic crystal structure of prisms 20, 21 may be produced byvarious other manufacturing processes. For example, prisms 20, 21 may beproduced utilizing stereolithography machines. In this case, the size,shape and spacing of holes 14 may be more elaborately defined to enablecloser approximations to the needed average index of refraction profile.Further, the shape and size of holes 14 may vary (e.g., non-circularshape and non-uniform hole dimensions). By way of example, the averageindex of refraction may be varied by selecting a spacing of holes andadjusting the hole diameters as a function of the distance from theprism edge. Moreover, stereolithography machines ease the task ofcreating layered structures that take into account the variation in theindex of refraction along the direction of propagation.

Referring back to FIG. 2, the use of a parent material with a highdielectric constant value for prism layer 10 results in a lighter prism,but tends to produce the prism without the property of being impedancematched. The lack of impedance matching creates surface reflections andultimately requires more power to operate an RF system. Accordingly,prisms 20, 21 include impedance matching layers 22 applied to photoniccrystal prism layer 10 to minimize these reflections. The idealdielectric constant of impedance matching layers 22 is the square-rootof the dielectric constant of prism layer 10. However, due to thevariable hole spacing in the prism layer as described above, thedielectric constant for the prism layer is variable.

In order to compensate for the variable dielectric constant of the prismlayer, impedance matching layers 22 similarly include a photonic crystalstructure. This structure may be constructed in the manner describedabove for the prism layer and includes a parent material 32 with anaverage dielectric constant approximating the square-root of the averagedielectric constant of parent material 12 used for prism layer 10. Theparent material may be of any shape or size and may be of any suitablematerials including the desired dielectric constant properties. By wayof example only, parent material 32 is substantially cylindrical in theform of a disk with substantially planar front and rear surfaces.

Impedance matching layers 22 typically include a hole-spacing patternsimilar to that for prism layer 10, but with minor variations to assurea correct square-root relationship between the local average dielectricconstant of the prism layer and the corresponding local averagedielectric constant of the impedance matching layers. In other words,the hole-spacing pattern is arranged to provide an average index ofrefraction (e.g., Equation 12) (or dielectric constant) profileequivalent to the square root of the average index of refraction (ordielectric constant) profile of the layer (e.g., prism layer 10) beingimpedance matched. In particular, the impedance matching layer thicknessis in integer increments of (2n−1)λ/4 waves or wavelength (e.g., ¼ wave,¾ wave, 5/4 wave, etc.) and is proportional to the square-root of theindex of refraction of the prism layer being impedance matched asfollows.

t√{square root over ( n (y))}=(2n−1)λ/4  (Equation 15)

where t is the impedance layer thickness, λ is the wavelength of thebeam of interest, n represents a series instance and n(y) is the averageindex of refraction of the prism layer as function of the distance, y,from the prism edge.

Achieving a lower index of refraction with an impedance matching layermay become infeasible due to the quantity of holes required in thematerial. Accordingly, systems requiring impedance matching layersshould start with an analysis of the minimum average index of refractionthat is likely to be needed for mechanical integrity, thereby providingthe index of refraction required for the impedance matching layer. Theaverage index of refraction of the device to which this impedancematching layer is mated would consequently be the square of the valueachieved for the impedance matching layer.

An ideal thickness for the impedance matching layers is one quarter ofthe wavelength of the signal of interest divided by the square-root ofthe (average) index of refraction of the impedance matching layer (e.g.,Equation 15, where the index of refraction is the square root of thedielectric constant as described above). Due to the variability of thedielectric constant of the impedance matching layer, a secondarymachining operation may be utilized to apply curvature to the impedancematching layers and maintain one quarter wave thickness from the layercenter to the layer edge. The impedance matching layers may enhanceefficiency on the order of 20%.

A typical illumination pattern on a dish antenna is a truncatedexponential field strength, or a truncated Gaussian. The Gaussian istruncated at the edge of the dish antenna since the field must getcut-off at some point. At the edge of the dish antenna, the fieldstrength must go to zero, yet for a typical feed horn arrangement, thefield strength at the edge of the dish antenna is greater than zero.This creates a problem in the far field, where the discontinuousderivative of the aperture illumination function creates unnecessarilystrong side-lobes. Side-lobes are the portion of an RF beam that aredictated by diffraction as being necessary to propagate the beam fromthe aperture of the antenna. In the far field, the main beam follows abeam divergence that is on the order of twice the beam wavelengthdivided by the aperture diameter. The actual intensity pattern over theentire far field, however, is accurately approximated as the Fouriertransform of the aperture illumination function.

Sharp edges in the aperture illumination function or any low-orderderivatives create spatial frequencies in the far field. These spatialfrequencies are realized as lower-power beams emanating from the RFantenna, and are called side-lobes. Side-lobes contribute to thedetectability of an RF beam, and make the beam easier to jam oreavesdrop. In order to reduce the occurrence of these types of adverseactivities, the side-lobes need to be reduced. One common technique toreduce side-lobes is to create an aperture illumination function that iscontinuous, where all of the function derivatives are also continuous.An example of such an illumination function is a sine-squared function.The center of the aperture includes an arbitrary intensity of unity,while the intensity attenuates following a sine-squared function of theaperture radius toward the outer aperture edge, where the intensityequals zero.

The sine-squared function is a simple function that clearly hascontinuous derivatives. However, other functions can be used, and mayoffer other advantages. In any event, the illumination function shouldbe chosen to include some level of absorption of the characteristic feedhorn illumination pattern (e.g., otherwise, gain would be required).

In order to reduce side-lobes, prism 20 may further include apodizingmask 24 that is truly absorptive for an ideal case. The apodizing maskis preferably constructed to include a photonic crystal structure (FIG.2) similar to the photonic crystal structures described above for theprism and impedance matching layers. In particular, holes 14 may bedefined within a parent material 42 with an appropriate absorptioncoefficient via any suitable techniques (e.g., drilling, etc.). Theholes are arranged or defined within the parent material to provide theprecise absorption profile desired. The parent material may be of anyshape or size and may be of any suitable materials including the desiredabsorbing properties. By way of example only, parent material 42 issubstantially cylindrical in the form of a disk with substantiallyplanar front and rear surfaces.

Material absorption is analyzed to provide the needed absorption profileas a function of beam radius (as opposed to the index of refraction).Holes 14 are placed in parent absorber material 42 to create an averageabsorption over a volume in substantially the same manner describedabove for achieving the average index of refraction profile for theprism layer. The actual function of the apodization profile may be quitecomplex if a precise beam shape is required. However, a simple formulaapplied at the edge of the aperture is sufficient to achieve a notablebenefit.

An example of an apodizing function that may approximate a desired edgeillumination taper for controlling side-lobes is one that includes 1/r²function, where r represents the radius of the beam or aperture. Forexample, a prism with an incident aperture illumination function that isGaussian in profile and an edge intensity of 20% (of the peak intensityat the center) may be associated with an edge taper function, ψ(r), asfollows.

$\begin{matrix}{{\psi (r)} = {\left( \frac{1}{3\left( {1 - r} \right)} \right)^{2} + 1}} & \left( {{Equation}\mspace{20mu} 16} \right)\end{matrix}$

The denominator multiplier term (e.g., three) is a consequence of theillumination function including 20% energy at the edge of the aperture.This multiplier may vary according to the energy value at the edge ofthe aperture. Equation 16 provides the absorption ratio as a function ofradius, which can be summarized as the ratio of the absorbed energy overthe transmitted energy. The value for the radius is normalized (e.g.,radius of r_(max)=1) for simplicity. This function closely approximatesthe ideal apodization function. However, minor variations to thefunction may be desired for an optimized system.

In order to realize this function within photonic crystal apodizing mask24, a series of holes 14 are placed within parent material 42 that ishighly absorptive to radio waves (e.g., carbon loaded material, etc.).The average absorption of the material (e.g., a weighted average of theabsorption of the material and holes (e.g., the holes should have noabsorption) based on volume and determined in a manner similar to theweighted average for the dielectric constant described above) over theinteraction volume of the prism provides the value of the absorption forthe apodizing mask. The mask absorption divided by the unapodized caseshould yield an approximate value resulting from Equation 16. Thus,holes 14 are placed in parent material 42 in a manner to provide theabsorption values to produce the desired absorption profile. Apodizingmask 24 may be configured with holes 14 closely spaced together whenthis layer is mounted to other layers of the prism. In this case, themechanical integrity for the apodizing mask is provided by the layers towhich the apodizing mask is mounted, thereby enabling the closely spacedarrangement of holes 14.

The apodizing mask is simple to manufacture through the use ofcomputer-aided fabrication techniques as described above. Equation 16may be modified to accommodate feeds that do not produce energydistributions with a Gaussian profile and achieve the desired results.

Prisms 20, 21 may be utilized to create virtually any type of desiredbeam pattern. The photonic crystal structure may be configured to createany types of devices (e.g., quasi-optical, lenses, prisms, beamsplitters, filters, polarizers, etc.) in substantially the same mannerdescribed above by simply adjusting the hole dimensions, geometriesand/or arrangements within a parent dielectric material to attain thedesired beam steering and/or beam forming characteristics. For example,a prism may be configured to include both lens and prism properties,where holes may be defined in the dielectric material to provide bothlens and prism properties. Beam steering device 50 may alternativelyemploy this type of photonic crystal structure including lens and prismproperties in place of prism 21 to steer and focus the RF beam. Thus,several photonic crystal structures may be produced each with adifferent hole pattern (e.g., including properties of prisms, lensesand/or other devices) to provide a series of interchangeable structures(e.g., prisms or other devices) for an RF beam steering system (FIG. 1).In this case, a photonic crystal prism may easily be replaced within thebeam steering device with other photonic crystal structures (e.g., withlens, prism and/or other desired properties) including different holepatterns to attain desired (and different) beam patterns and/orsteering.

The present invention embodiments may be utilized in varyingapplications. For example, the present invention embodiments may beutilized for moderate levels of radio beam deflection (e.g., such asthat offered by a pan-tilt positioner) when the combined antenna/prismassembly is mounted on a conventional (e.g., azimuth-only) rotator(e.g., such as a Yaesu G-1000DXA or similar unit). Further, the presentinvention embodiments may be utilized for moderate levels of radio beamdeflection in systems that are impractical to implement usingtraditional phased-array or gimbal steering techniques. Moreover, thepresent invention embodiments may be applied for spatial separation ofradio beams, each at different frequencies, to an array offrequency-specific generators or detectors.

In addition, the present invention embodiments may be advantageous formast-mounted scenarios (e.g., a mast on a motorized or other vehicle(e.g., ground vehicle, etc.)) since the photonic crystal prisms providegreatly reduced mechanical coupling. For example, the mechanicalcoupling within conventional azimuth/elevation compensation systemstends to cause added sway in mast-mounted scenarios that may become arun-away problem. The photonic crystal prisms of the present inventionembodiments employ greatly reduced coupling and may be advantageous inmobile applications including swaying antenna masts that would otherwisebe too problematic for conventional systems, especially for higherfrequency antennas that include greater directionality.

Even with the greatly reduced coupling of embodiments of the presentinvention, undesirable swaying in certain configurations, e.g.,mast-mounted configurations, may still occur. That is, both prisms 20,21 may undesirably move together along with a platform to which theprisms are mounted. To address any mis-steering as a consequence of suchmotion, sensors 29 (FIG. 1) may also include accelerometer (or tilt)sensors mounted in the vicinity of prisms 20, 21. Such sensors may beused to compensate for any instability in the platform to which the beamsteering device 50 is mounted and thereby provide a more stabilized RFbeam.

More specifically, a sensor 29 associated with prism 20 may bedesignated, mounted and/or configured to sense left/right (or roll)motion of the platform, and a sensor 29 associated with prism 21 may beassigned, mounted and/or configured to sense forward/backward (or pitch)motion of the platform. In such a configuration, the two accelerometersneed only be single-axis sensors. However, those skilled in the art willappreciate that multi-axis accelerometers are readily available in themarket (e.g., from Analog Devices, Norwood, Mass.) and thus thedescribed two single-axis accelerometer embodiment may, alternatively,be replaced with a single two-axis sensor embodiment. Alternatively, aplurality of multi-axis sensors may be employed for purposes ofredundancy and/or compensation. As shown in FIG. 1, sensors 29 may bemounted directly on motors 30, or may be mounted spaced from motors 30.Yaw may also be monitored. Ultimately, specific design considerations,cost, and other factors will dictate whether single or multi-axisaccelerometers (and how many) are to be implemented and precisely wheresuch sensors should be located.

FIG. 7 depicts a block diagram of an exemplary circuit 700 (parts ofwhich may be embodied in controller 40 of FIG. 1) in accordance with anembodiment of the present invention. As shown, a microcontroller 730 ispowered through a power converter 710, as necessary, and is configuredto send commands to motor drivers 750 that respectively drive motors 30to adjust the orientation of prisms 20, 21. An external commandinterface may also be provided to, e.g., provide access tomicrocontroller to reprogram or debug the same.

As further shown in FIG. 7, signals (e.g., analog voltage signals ordigital signals) from accelerometer sensors 29 are provided ortransmitted (e.g., wirelessly) to microcontroller 730. The signals arerepresentative of acceleration forces detected by the sensors.Microcontroller 730 then processes the received signals and translatesthe same into appropriate commands to motor drivers 750, which, in turn,drive motors 30 to rotate prisms 20, 21 in an appropriate direction tocompensate for, e.g., sway that has been detected by the sensors.

A temperature compensation sensor 770 may also be provided to monitorambient temperature and provide information to microcontroller 730sufficient to account for changes, e.g., drift, in the signals receivedfrom sensors 29.

FIG. 8 illustrates a more mechanical approach to compensation for, e.g.,swaying, or for other stabilization needs. In this embodiment, insteadof using tilt or accelerometer sensors, counterweights 810, 820 areprovided. Such counterweights may be in the form of a pendulum, but anyshape that provides sufficient weight and suitable reaction time may beemployed. In the case of left/right motion, counterweight 810 may bedirectly (or indirectly) coupled to prism 20 such that any swaying willbe dampened by the counterweight. In the case of forward/backwardmotion, counterweight 820 may be coupled to prism 21 via a right-anglegear drive mechanism 830, since forward/backward motion occurs in aplane that is perpendicular to a plane in which prism 21 rotates. Inthis embodiment, it may be desirable to have a clutch mechanism (notshown) for motors 30 such that after prisms 20, 21 are rotated todesired positions, the motors are disengaged and the mechanicalcompensation technique is thereafter permitted to control theorientation of the prisms. Counterweights 810, 820 could also be used aspart of an electromechanical tilt device, signals from which could bepassed to microcontroller 730.

In sum, it may be desirable to include a compensation or stabilizationdevice or technique to the beam steering methodologies and devicesdescribed herein to compensate for movement, such as mast swaying, and,in effect, stabilize, or further steer the RF beam 7.

It will be appreciated that the embodiments described above andillustrated in the drawings represent only a few of the many ways ofimplementing a method and apparatus for steering radio frequency beamsutilizing photonic crystal structures.

The prisms may each include any quantity of layers arranged in anysuitable fashion. The layers may be of any shape, size or thickness andmay include any suitable materials. The prisms may be utilized forsignals in any desired frequency range. The prism layer may be of anyquantity, size or shape, and may be constructed of any suitablematerials. Any suitable materials of any quantity may be utilized toprovide the varying dielectric constants (e.g., a plurality of solidmaterials, solid materials in combination with air or other fluid,etc.). The prism layer may be utilized with or without an impedancematching layer and/or apodizing mask. The prism layer parent and/orother materials may be of any quantity, size, shape or thickness, may beany suitable materials (e.g., plastics (e.g., a high densitypolyethylene, etc.), RF laminate, glass, etc.) and may include anysuitable dielectric constant for an application. The parent materialpreferably includes a low loss tangent at the frequency range ofinterest. The prism layer may be configured (or include several layersthat are configured) to provide any desired steering effect or angle ofrefraction or to emulate any properties of a corresponding material oroptical prism, lens and/or other beam manipulating device. The prismlayer may further be configured to include any combination of beamforming (e.g., lens) and/or beam steering (e.g., prism) characteristics.

The holes for the prism layer may be of any quantity, size or shape, andmay be defined in the parent and/or other material in any arrangement,orientation or location to provide the desired characteristics (e.g.,beam steering effect, index of refraction, dielectric constant, etc.).The various regions of the prism layer parent material may include anydesired hole arrangement and may be defined at any suitable locations onthat material to provide the desired characteristics. The holes may bedefined within the parent and/or other material via any conventional orother manufacturing techniques or machines (e.g., computer-aidedfabrication techniques, stereolithography, two-dimensional machines,waterjet cutting, laser cutting, etc.). Alternatively, the prism layermay include or utilize other solid materials or fluids to provide thevarying dielectric constants.

The impedance matching layer may be of any quantity, size or shape, andmay be constructed of any suitable materials. Any suitable materials ofany quantity may be utilized to provide the varying dielectric constants(e.g., a plurality of solid materials, solid materials in combinationwith air or other fluid, etc.). The parent and/or other materials of theimpedance matching layer may be of any quantity, size, shape orthickness, may be any suitable materials (e.g., plastics (e.g., a highdensity polyethylene, etc.), RF laminate, glass, etc.) and may includeany suitable dielectric constant for an application. The parent materialpreferably includes a low loss tangent at the frequency range ofinterest. The impedance matching layer may be configured (or includeseveral layers that are configured) to provide impedance matching forany desired layer of the prism.

The holes for the impedance matching layer may be of any quantity, sizeor shape, and may be defined in the parent and/or other material in anyarrangement, orientation or location to provide the desiredcharacteristics (e.g., impedance matching, index of refraction,dielectric constant, etc.). The holes may be defined within the parentand/or other material via any conventional or other manufacturingtechniques or machines (e.g., computer-aided fabrication techniques,stereolithography, two-dimensional machines, waterjet cutting, lasercutting, etc.). Alternatively, the impedance matching layer may includeor utilize other solid materials or fluids to provide the varyingdielectric constants.

The apodizing mask may be of any quantity, size or shape, and may beconstructed of any suitable materials. Any suitable materials of anyquantity may be utilized to provide the desired absorption coefficientor absorption profile (e.g., a plurality of solid materials, solidmaterials in combination with air or other fluid, etc.). The parentand/or other material of the apodizing mask may be of any quantity,size, shape or thickness, may be any suitable materials (e.g., plastics(e.g., a high density polyethylene, etc.), RF laminate, carbon loadedmaterial, etc.) and may include any suitable radio or other waveabsorption characteristics for an application. The parent material ispreferably implemented by a material highly absorptive to radio waves.The apodizing mask may be configured (or include several layers that areconfigured) to provide the desired absorption profile.

The holes for the apodizing mask may be of any quantity, size or shape,and may be defined in the parent and/or other material in anyarrangement, orientation or location to provide the desiredcharacteristics (e.g., side-lobe suppression, absorption, etc.). Theholes may be defined within the parent and/or other material via anyconventional or other manufacturing techniques or machines (e.g.,computer-aided fabrication techniques, stereolithography,two-dimensional machines, water jet cutting, laser cutting, etc.).Alternatively, the apodizing mask may include or utilize other solidmaterials or fluids to provide the absorption properties. The apodizingmask may be configured to provide the desired absorbing properties forany suitable taper functions.

The layers of the prism (e.g., prism layer, impedance matching,apodizing mask, etc.) may be attached in any fashion via anyconventional or other techniques (e.g., adhesives, etc.). The prism maybe utilized in combination with any suitable signal source (e.g., feedhorn, antenna, etc.), or signal receiver to steer incoming signals. Theprism or other photonic crystal structure may be utilized to createvirtually any type of desired beam pattern, where several prisms orstructures may be produced each with a different hole pattern to providea series of interchangeable structures to provide various beams for RFor other systems. Further, the photonic crystal structure may beutilized to create any beam manipulating device (e.g., prism, lens, beamsplitters, filters, polarizers, etc.) by simply adjusting the holedimensions, geometries and/or arrangement within the parent and/or othermaterials to attain the desired beam steering and/or beam formingcharacteristics.

The beam steering device may include any quantity of components (e.g.,motors, rotating assemblies, controller, sensors, etc.) arranged in anydesired fashion. The beam steering device may employ any quantity ofprisms and/or other beam manipulating devices arranged and/or orientedin any desired fashion to steer any type of beam in any desired manner.The rotating assemblies may be of any quantity, shape or size and may beimplemented by any conventional or other assemblies. The rotatingassemblies may include any suitable rotating mechanism (e.g., rotatingring, platform or other suitable structure) to secure and rotate a beammanipulating device (e.g., prism, etc.) and may be disposed at anysuitable locations. The rotating assemblies may manipulate the beamsteering devices (e.g., prism, etc.) to any suitable orientations tosteer the beam in a desired manner. The motors may be of any quantity,shape or size and may be implemented by any conventional or other motorsor actuators to rotate the beam manipulating devices (e.g., prism,etc.).

The controller may be of any quantity and may be implemented by anyconventional or other controller or processor (e.g., microprocessor,controller, control circuitry, logic, etc.). The sensors may be of anyquantity and may be implemented by any conventional or other sensors(e.g., encoders, potentiometers, etc.) to measure the rotation of thebeam manipulating devices (e.g., prism, etc.) and/or other systemconditions. The sensors may be disposed at any suitable locations tomeasure the rotation (e.g., motors, rotating assemblies, etc.) of thebeam manipulating devices (e.g., prism, etc.). The beam steering devicemay be employed with any suitable signal source (e.g., antenna, feedhorn, etc.) or RF system to provide the desired beam steering, where thebeam steering device may be positioned at any suitable location toreceive and steer a beam.

It is to be understood that the terms “top”, “bottom”, “front”, “rear”,“side”, “height”, “length”, “width”, “upper”, “lower”, “thickness”,“vertical”, “horizontal” and the like are used herein merely to describepoints of reference and do not limit the present invention embodimentsto any particular orientation or configuration.

From the foregoing description, it will be appreciated that theinvention makes available a novel method and apparatus for steeringradio frequency beams utilizing photonic crystal structures, wherein abeam steering device utilizes photonic crystal structures (e.g., prisms,etc.) to steer or direct RF beam transmissions.

Having described preferred embodiments of a new and improved method andapparatus for steering radio frequency beams utilizing photonic crystalstructures, it is believed that other modifications, variations andchanges will be suggested to those skilled in the art in view of theteachings set forth herein. It is therefore to be understood that allsuch variations, modifications and changes are believed to fall withinthe scope of the present invention as defined by the appended claims.

1. An apparatus for manipulating a radio frequency (RF) beam,comprising: a platform; a first prism mounted on the platform; a secondprism mounted on the platform; a controller that rotates the first prismand the second prism to steer an RF beam that is transmittedsuccessively through the first prism and the second prism; and acompensation device configured to compensate for movement of theplatform by further rotating the first prism and the second prism inresponse to the movement of the platform.
 2. The apparatus of claim 1,wherein the first prism and the second prism each comprises a photoniccrystal structure that respectively produce an electromagnetic field tosteer the RF beam.
 3. The apparatus of claim 1, wherein the compensationdevice comprises an accelerometer.
 4. The apparatus of claim 3, furthercomprising a temperature compensation sensor.
 5. The apparatus of claim1, wherein the compensation device comprises a tilt sensor.
 6. Theapparatus of claim 1, wherein the compensation device comprises acounterweight coupled to at least one of the first prism and the secondprism.
 7. The apparatus of claim 6, wherein the compensation devicefurther comprises a right-angle drive.
 8. The apparatus of claim 6,wherein the counterweight is in the form of a pendulum.
 9. The apparatusof claim 1, wherein the apparatus is mounted on mast.
 10. The apparatusof claim 1, wherein at least one of the first prism and the second prismincludes a refraction layer including a photonic crystal structure torefract the RF beam, and at least one impedance matching layer toimpedance match the refraction layer.
 11. An apparatus for manipulatinga radio frequency (RF) beam comprising: a first beam manipulatingassembly including a first beam manipulating device to refract said RFbeam, wherein said first beam manipulating device includes a firstphotonic crystal structure that produces an electromagnetic field torefract said RF beam; a second beam manipulating assembly including asecond beam manipulating device to steer said refracted RF beam fromsaid first beam manipulating device at a desired angle, wherein saidsecond beam manipulating device includes a second photonic crystalstructure that produces an electromagnetic field to steer said RF beam;and a compensation device to compensate for a combined movement of saidfirst and second beam manipulating assemblies, wherein said first andsecond beam manipulating assemblies orient said first and second beammanipulating devices relative to each other to steer said RF beam atsaid desired angle.
 12. A method of manipulating a radio frequency (RF)beam, comprising: refracting said RF beam by producing anelectromagnetic field via a first photonic crystal structure within afirst beam manipulating device; steering said refracted RF beam fromsaid first beam manipulating device at a desired angle by producing anelectromagnetic field via a second photonic crystal structure within asecond beam manipulating device; orienting said first and second beammanipulating devices relative to each other to steer said RF beam atsaid desired angle; sensing a combined movement of said first photoniccrystal structure within said first beam manipulating device and saidsecond photonic crystal structure within said second beam manipulatingdevice; and compensating for the combined movement by further orientingsaid first and second beam manipulating devices relative to each other.13. The method of claim 12, wherein sensing the combined movementcomprises receiving signals from an accelerometer.
 14. The method ofclaim 13, further comprising compensating for an effect of temperatureon the accelerometer.
 15. The method of claim 12, wherein sensing thecombined movement comprises monitoring a tilt sensor.
 16. The method ofclaim 12, wherein compensating for the combined movement comprisesdriving a motor associated with at least one of said first and secondbeam manipulating devices.
 17. The method of claim 12, whereincompensating for the combined movement comprises responding to acounterweight associated with at least one of said first and second beammanipulating devices.